Having just been sent away to live with his uncle and aunt in Indiana, teenager Sparke Thornton (Lon McCallister) has a penchant for trouble. At first, he is not satisfied with the arrangement, and continues to express his rebellious behavior. Already on his first day, he plans on running away, but crossing a harness racing track convinces him to stay in Indiana. The owner, Godaw Boole (Charles Dingle) welcomes Sparke, and introduces him to Char Bruce (Jeanne Crain), a tomboyish girl who loves to race horses. A servant (George Reed) informs him that his uncle Thunder Bolt (Walter Brennan) was once part of harness horse racing as a respected sulky driver.